1. Field of the Invention
The invention pertains to a honeycomb body, particularly a catalyst carrier body, which is formed of at least partly structured metal sheets defining a plurality of channels through which a fluid can flow.
2. Description of the Related Art
It is known from German published, non-prosecuted application 23 21 378 to produce honeycomb bodies from a ribbon of sheet metal, by providing the sheet-metal ribbon with fold lines, folding it, and inserting it into a cylindrical case. The ribbon is disposed around a center, and both the outer circumferential segments pointing toward the center of the ribbon and those pointing outward form circles. The sheet-metal ribbon itself remains uncorrugated, so that overall, only a few flow channels of large cross section are formed in the honeycomb body. The sheet-metal is covered with catalyst material. A cylindrical void that cannot be utilized for the catalytic conversion process remains in the interior of the metal carrier.
From European application EP 245 737 (corresponding to U.S. Pat. Nos. 4,832,998 and 4,923,109), it is known to produce honeycomb bodies from a number of individual sheet-metal layers. Alternating corrugated and smooth sheet-metal segments are layered into a stack. The stack is then intertwined around two fixed points, producing a honeycomb body whose sheet-metal layers are arranged approximately in the shape of an S. This is the so-called S-form catalyst.
From German published, non-prosecuted application 33 41 868 (corresponding to U.S. Pat. No. 4,647,435), it is known to produce a honeycomb body from a sheet-metal strip folded on itself in a meandering or zig-zag fashion. The strip is provided with prefabricated crease lines at the folding points.
The known prior art has numerous disadvantages. In German 23 21 378, for instance, the catalytically active surface area is too small; especially for use in motor vehicles, a considerably larger catalyst surface area, with simultaneously very compact outer dimensions, are desired. In EP 245 737, the honeycomb body is produced from individual sheet-metal segments. The handling of these segments is problematic, however, because the sheets are very thin and have a very smooth surface and hence can easily stick together. In production, particular care must be taken in this respect. While German 33 41 868 avoids a number of these disadvantages, the honeycomb body is very rigid, so that it does not always withstand thermal strains. Moreover, the way in which the zig-zag layers are folded on one another is very labor-intensive.
European application EP 0 245 736 discloses a honeycomb body in which the individual sheet-metal layers have an involute course in the outer region. This leads to a very uniform structure and great durability in the face of thermal strains. The international publication WO 90/03220 (corresponding to U.S. Pat. Nos. 5,105,539; 5,135,794; and 5,139,844), from which the instantly disclosed invention starts out, also discloses an especially favorable method for producing such honeycomb bodies. Three or more stacks of sheets, which are at least partly structured, are intertwined with one another.
The configurations have many advantages, particularly since the forces due to alternating thermal strains are uniformly distributed in the honeycomb body. One of the disadvantages, as must be pointed out, however, is that many sheets have to be cut to a suitable length and then stacked into stacks. The individual sheet-metal layers are also not long enough that electric conductors of sufficient length for heating the honeycomb body or for representative measurement over the entire cross section can be integrated into a single such sheet.
International publication WO 91/14855 also discloses a honeycomb body having at least one integrated electric conductor. When the conductor is laid in a simple, straight course, it can have only a limited length.